1. Field of the Invention
The present invention relates to an ink jet recording apparatus for recording on a recording material by discharging ink from recording means.
2. Related Background Art
A recording apparatus, which is provided to function as a printer, a copying machine, or a facsimile machine, or used as an output device for a work station or a complex electronics apparatus including a computer or word processor, is structured to record on a recording medium, such as a recording sheet or thin plastic plate, images that include characters, drawings, and the like in accordance with image information including information on characters, drawings, and the like. The recording apparatus is classified into ink jet type, wire-dot type, thermal type, laser beam type, or some other type. Of those recording apparatuses, the recording apparatus of ink jet type (hereinafter may be referred to also as an ink jet recording apparatus) performs recording by discharging ink from recording means (hereinafter may be referred to also as a recording head) to a recording medium, and this recording means has such excellent advantages as to make it easier to record in higher precision at higher speed with a lesser amount of noise, and at lower cost than the other types.
Also, in recent years, there has been an increasing need for a recording apparatus capable of outputting highly precise color images, and there have been developed, too, various color ink jet recording apparatuses capable of recording color images by discharging ink of plural colors.
In such an ink jet recording apparatus, a recording head having a plurality of recording elements integrally arranged is used for improving a recording speed. As for that recording head, it is generally practiced that a plurality of integrally formed ink discharge ports and liquid flow paths are used for the ink discharge portion. Also, for color recording, a plurality of the aforesaid recording heads are provided.
FIG. 1 is a view that shows the structure of the printing unit used for printing by the aforesaid recording head on the surface of a recording sheet. In FIG. 1, each structure designated by a reference numeral 101 is an ink cartridge. Each of them is formed by an ink tank containing one of four colors, black, cyan, magenta, and yellow, respectively, as well as by a recording head 102. For the recording head 102, the discharge port array is formed with a plurality of discharge ports. FIG. 2 is a view that schematically shows the state of the plurality of discharge ports arranged for the recording head 102, observed in the direction indicated by z in FIG. 1. In FIG. 2, a reference numeral 201 designates a plurality of discharge ports arranged on the recording head 102.
Also, in FIG. 1, a reference numeral 103 designates a sheet conveying roller that conveys the recording sheet P in the direction y, as required, by rotating in the direction indicated by an arrow in FIG. 1, while pressing the recording sheet P in cooperation with an auxiliary roller 104. Also, a reference numeral 105 designates a sheet feed roller for feeding a recording sheet, while pressing the recording sheet P in the same manner as the rollers 103 and 104. A reference numeral 106 designates a carriage to support the four ink cartridges, and allows printing by enabling them to travel. The carriage is arranged to be on standby in the home position h indicated by dotted line in FIG. 1 when printing is at rest or operating the recovery of the recording head or the like.
The carriage 106 in the home position before the initiation of printing is caused to travel in the direction indicated by an arrow X in FIG. 1 when the command to begin printing is received, while discharging ink from a plurality of discharge ports 201 formed on the discharge port surface of the recording head 102 for recording in accordance with recording data. Then, when printing of data is completed up to the edge portion of the recording sheet, the carriage returns to the original home position and again performs printing while traveling in the direction X.
When pictorial images are printed, various elements, such as coloring, gradation, and evenness, are required. Particularly, for evenness, slight variations of nozzles per unit that may take place in the manufacturing process of a recording head tend to exert influence on the ink discharge amount of each nozzle and the discharging direction thereof in the printing operation, and it is known that the degradation of image quality is brought about by this influence eventually as density unevenness of printed image.
Here, the specific example thereof will be described in conjunction with FIGS. 3 and 4. At (1) in FIG. 3, a reference numeral 31 designates the recording head schematically. The nozzle array provided for the recording head 31 is formed by eight nozzles 32. Also in FIG. 3, a reference numeral 33 designates an ink droplet discharged from the nozzle 32 (hereinafter, may be referred to also as xe2x80x9cink dropletxe2x80x9d or simply as xe2x80x9cinkxe2x80x9d). Also, (2) in FIG. 3 shows one example of the image that is formed by ink discharged periodically from the nozzle array of the recording head 31. (2) in FIG. 3 represents the example, in which recording is performed with eight dots per each nozzle, while the recording head is being moved. (3) in FIG. 3 is a graph that shows the optical density of the image represented at (2) in FIG. 3. At (3) in FIG. 3, the axis of abscissa corresponds to the density.
Ideally, each ink droplet discharge from the recording head 31 should be in the same amount and direction as shown at (1) in FIG. 3. If discharge is made ideally like this, dots of the same size are impacted on the surface of recording sheet as shown at (2) in FIG. 3. As a result, then, it becomes possible to obtain an image having no unevenness in overall density as shown at (3) in FIG. 3.
However, as described earlier, there are actually variations in individual nozzles, and if ink is discharged for printing without compensation, density unevenness is created due to the variations of the size of each ink droplet discharged from each nozzle and the direction thereof.
FIG. 4 is a view that schematically illustrates density unevenness when there are variations in a plurality of nozzles of the recording head. (1) to (3) in FIG. 3 correspond to (1) to (3) in FIG. 4, respectively. In comparison with each other, it is possible to compare each condition of recording when it is ideally performed and when it is performed with the nozzles having individual variations.
(1) in FIG. 4 shows the recording head, and the state where there are variations in the size and direction of each of the ink droplets discharged from the recording heads. As shown at (1) in FIG. 4, when the size and direction of each ink droplet discharged for each nozzle are varied, each of them is impacted on the surface of the recording sheet as shown at (2) in FIG. 4. According to (2) in FIG. 4, there exist periodically the blank portion on the recording sheet where the area factor is not satisfied 100% with respect to the head main scanning direction, or on the contrary, dots are overlapped more than necessary or as shown in the central part of (2) in FIG. 4, a white streak occurs. The gathering of dots thus impacted presents the density distribution as shown at (3) in FIG. 4 with respect to the direction of the nozzle array. As a result, these phenomena are sensed as density unevenness as far as the normal human eyesight is concerned. Also, there may be some cases where streaks become conspicuous due to the variations that may take place in the amount of sheet feeding.
To cope with the density unevenness described above, a method for reducing density unevenness is disclosed in the specification of Japanese Patent Application Laid-Open No. 06-143618. With reference to FIG. 5, such method will be described briefly hereunder.
The recording operation shown in FIG. 5 is completed by enabling the recording head 31 to scan three times in the recording area shown at (2) in FIG. 3 and (2) in FIG. 4, and at (1) in FIG. 5 the relative positions of the recording head 31 at the first, second, and third scans are shown. In this recording operation, the recording head 31 and the recording sheet are relatively moved in the sub-scanning direction (at (1) in FIG. 5, the nozzle arrangement direction of the recording head) per scanning of the recording head. Also, the amount of the relative movement is the one corresponding to half of eight nozzles provided for the recording head 31.
According to the recording operation shown in FIG. 5, the recording head 31 performs the main scans three times in the printing area shown at (2) in FIG. 3 and (2) in FIG. 4, but a half of the printing area, that is, an area corresponding to four nozzles, is completed by the scanning of the recording head two times (hereinafter referred to as a two-pass). In this case, the eight nozzles of the recording head are divided into two groups, that is, the upper side four nozzles and the lower side four nozzles. Then, the dots printed by one nozzle per main scan are those which are regular image data thinned approximately by half in accordance with a certain designated image data arrangement. Then, dots are covered in the remaining half of the image data when the second main scanning is performed in order to complete printing in the unit area of four pixels. The recording method described above is called a multi-pass recording method hereunder. In this respect, the recording method shown in FIG. 5 may be called a two-pass recording method, because a designated area is completed by a two-time scanning.
With a recording method of the kind, even if the same recording head as shown at (1) in FIG. 4 is used, the influence of each nozzle per se that may be exerted on the printing image is reduced by half. The printed image becomes as shown at (2) in FIG. 5, and such black streaks and white streaks as shown at (2) in FIG. 4 are no longer too conspicuous. Therefore, the density unevenness becomes less conspicuous as shown at (3) in FIG. 5 as compared with the case shown at (3) in FIG. 4. When a recording of the kind is performed, the first main scan and the second main scan are divided in a form of complementing each other in accordance with a certain designated arrangement of image data. Usually, here, it is most common that this image data arrangement is used in the form of checkered flag pattern having every other pixel arranged vertically and horizontally in it as shown in FIGS. 6A to 6C. Consequently, in the printing area per unit (here, in a unit of four pixels), recording is completed with the first main scan that records the a checkered flag pattern, and the second main scan that records the reverse checkered flag pattern (the reverse pattern of the first scan). Each of FIGS. 6A to 6C illustrates the way in which a designated area is recorded by use of the checkered flag- and reverse checkered flag-thinning patterns, respectively. Here, in FIGS. 6A to 6C, reference numerals 31a, 31b, and 31c designate the relative positions of the recording head 31 in the first, second, and third scans, respectively.
In FIGS. 6A to 6C, at first in the first main scan, the checkered flag-thinning pattern is recorded by use of the lower four nozzles (FIG. 6A). Then, in the second main scan, the recording sheet is fed for a portion of four pixels (xc2xd of the head length), and the reverse checkered flag-thinning pattern is recorded (FIG. 6B). Further, in the third main scan, the recording sheet is again fed for a portion of four pixels (xc2xd of the head length) and the checkered flag-thinning pattern is again recorded (FIG. 6C). In this way, the sheet feeding per four-pixel unit and the checkered flag and reverse checkered flag patterns are recorded alternately to complete the recording area of four-pixel unit per main scan.
As described above, with the completion of the image in the same area by different nozzles one after another, it is made possible to obtain a high quality image having no density unevenness.
Also, there is disclosed in the specification of Japanese Patent Laid-Open Application No. 06-135014 to obtain a high quality image by preventing the occurrence of bleeding on the adjacent boundaries of a black image and a color image. To describe such art briefly, when a black image printed in black ink and a color image printed in color ink are adjacent to each other, a designated discharge portion is used among the discharge group for black ink discharge so that scanning for the formation of a black image (scanning in the direction X described above) is not made to scan continuously for recording a color image (scanning in the direction X as described above). In this way, bleeding on the adjacent boundaries of a black image and a color image is prevented so as to attain recording of a high quality image.
However, there is no disclosure in the specification of the aforesaid Japanese Patent Application Laid-Open No. 06-135014 as to the multi-pass recording or recording provided with the setting of two or more kinds of amounts for conveying a recording sheet.
With attention to the bleeding between colors in the aforesaid multi-pass recording method, studies have been made. It is found that when the multi-pass recording method is adopted, the bleeding has characteristics different from those encountered in the case where an image is completed by one-time scanning of a recording head.
Also, in addition to the bleeding, it is found that there is difference between the one-pass recording method and the multi-pass recording method in the phenomenon that the recorded portion becomes whitish due to the ink droplets pushing each other on a recording medium when ink of plural colors is impacted on the surface of the recording medium. The difference in such phenomenon is caused by the permeating and fixing conditions of ink on a recording medium, which are different between them, because the multi-pass recording method has a smaller number of dots to be recorded per unit time on a designated area, besides the effect of the multi-pass recording method for the prevention of density unevenness.
Also, as regards the recording, which is provided with the setting of two or more kinds of conveying amounts of a recording medium, it is observed that if each of the image areas is completed by discharging ink from at least two kinds or sets of discharge port arrays using the multi-pass recording method, color unevenness occurs between areas where time difference takes place in the completion of images within the overlapped image area that contains the first image area to be completed by the first discharge port array and the second image area to be completed by the second discharge port array. Here, in the first image area completed by the first discharge port array, the permeation and ink fixing on the recording medium are caused to change as the time elapses. Therefore, if ink is discharged from the second discharge port array to overlap it or place it adjacent to the first image area the conditions of which are being changed as the time elapses, the permeation and fixing conditions of the overlapped or adjacent ink on the recording medium are made different according to the time required for completing such change of states. This is the phenomenon that may cause the occurrence of such color unevenness as described above.
It is an object of the present invention to provide an ink jet recording apparatus capable of reducing the bleeding between colors created characteristically by the multi-pass recording method, and also, capable of preventing color unevenness from being created by a recording method provided with two or more kinds of conveying amounts of a recording medium for recording high quality images.
To solve the problems discussed above, an ink jet recording apparatus of the present invention records by discharging ink while the recording head thereof executes the main scans relatively to a recording medium, and provided with at least two kinds of discharge port arrays having a plurality of ink discharge ports arranged in the direction different from the aforesaid main scanning direction, and also, provided with a recording method in which the number of recording scans in the main scanning direction is m (m: a positive integer) to complete an image by a first discharge port array, and the number of recording scans in the main scanning direction is n (n: a positive integer) to complete the image by a second discharge port array, and at least two kinds of one-time conveying amounts for conveying the recording medium in the sub-scanning direction per main scan. Then, with respect to the first discharge port array, the second discharge port array makes the position of the leading end portion of the discharge ports used from the side of the sheet feeding direction for feeding the recording medium equal to the length of the continuously conveying amount of (m+a) (a: a positive integer) times using at least the aforesaid two kinds of conveying amounts.
Also, an ink jet recording apparatus of the present invention records by discharging ink while the recording head thereof executes the main scans relatively to a recording medium, and provided with at least two kinds of discharge port arrays having a plurality of ink discharge ports arranged in the direction different from the aforesaid main scanning direction, and also, provided with a recording method in which the number of recording scans in the main scanning direction is m (m: a positive integer) to complete an image by a first discharge port array, and the number of recording scans in the main scanning direction is n (n: a positive integer) to complete the image by a second discharge port array, and at least two kinds of one-time conveying amounts for conveying the recording medium in the sub-scanning direction per main scan. Then, with respect to the first discharge port array, the second discharge port array makes the position of the leading end portion of the discharge ports used from the side of sheet expelling direction for expelling the recording medium equal to the length of the continuously conveying amount of (m+a) (a: a positive integer) times using at least the aforesaid two kinds of conveying amounts.
Also, an ink jet recording apparatus of the present invention records by discharging ink while the recording head thereof executes the main scans relatively to a recording medium, and provided with at least two kinds of discharge port arrays having a plurality of ink discharge ports arranged in the direction different from the aforesaid main scanning direction, and also, provided with a recording method in which the number of recording scans in the main scanning direction is m (m: a positive integer) to complete an image by a first discharge port array, and the number of recording scans in the main scanning direction is n (n: a positive integer) to complete the image by a second discharge port array, and at least two kinds of one-time conveying amounts for conveying the recording medium in the sub-scanning direction per main scan. Then, with respect to the first discharge port array, the second discharge port array makes the position of the leading end portion of the discharge ports used from the side of sheet feeding direction for feeding the recording medium larger than the length of the continuously conveying amount of (m+a) (a: a positive integer) times and smaller than the length of the continuously conveying amount of (m+a+1) using at least the aforesaid two kinds of conveying amounts.
Also, an ink jet recording apparatus of the present invention records by discharging ink while the recording head thereof executes the main scans relatively to a recording medium, and provided with at least two kinds of discharge port arrays having a plurality of ink discharge ports arranged in the direction different from the aforesaid main scanning direction, and also, provided with a recording method in which the number of recording scans in the main scanning direction is m (m: a positive integer) to complete an image by a first discharge port array, and the number of recording scans in the main scanning direction is n (n: a positive integer) to complete the image by a second discharge port array, and at least two kinds of one-time conveying amounts for conveying the recording medium in the sub-scanning direction per main scan. Then, with respect to the first discharge port array, the second discharge port array makes the position of the leading end portion of the discharge ports used from the side of sheet expelling direction for expelling the recording medium larger than the length of the continuously conveying amount of (m+a) (a: a positive integer) times and smaller than the length of the continuously conveying amount of (m+a+1) using at least the aforesaid two kinds of conveying amounts.
Also, in accordance with the present invention, at least one of the positions of the discharge ports used for one main scan to complete an image by the aforesaid first discharge port array and the discharge ports used for one main scan to complete the image by the aforesaid second discharge port array is made different according to the combination of the continuously conveying amount of the aforesaid (m+a) (a: a positive integer) times including the next conveying amount.